2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/524A new determination of the pregalactic helium abundance based on the Magellanic Clouds H II regions is discussed. This determination amounts to Yp = 0.2345 +- 0.0030 and is compared with those derived from giant extragalactic H II regions in systems with extremely low heavy elements content. It is suggested that the higher primordial value derived by other authors from giant H II region complexes could be due to two systematic effects: the presence of neutral hydrogen inside the helium Stromgren sphere and the presence of temperature variations inside the observed volume.10 pages, 1 figure, IAU Symposium 198Astrophysicstext